@article{ZVMMF_1978_18_2_a6,
     author = {Pham Huu Sach},
     title = {The support principle in a general extremum problem},
     journal = {\v{Z}urnal vy\v{c}islitelʹnoj matematiki i matemati\v{c}eskoj fiziki},
     pages = {338--350},
     publisher = {mathdoc},
     volume = {18},
     number = {2},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZVMMF_1978_18_2_a6/}
}